In tyre manufacturing, cements are normally organic-solvent-based. Cements of this sort are highly adhesive and easy to use, mainly on account of rubber dissolving readily in organic solvents and so blending with other rubber to form practically one piece once the organic solvent evaporates.
For environmental reasons, recent European directives have imposed a drastic reduction in the use of organic solvents in the tyre industry, thus forcing manufacturers to devise alternative solutions to ensure correct adhesion of rubber layers.
One alternative to traditional cements is water-based cements, in which organic solvent is replaced by water as solvent, and which poses the problem of ensuring dispersion in water of intrinsically hydrophobic ingredients. This is done using emulsifiers which, as is known, comprise a hydrophobic group capable of bonding the ingredient in question, and a hydrophilic group capable of ensuring its dispersion in water. Since emulsifiers are normally selectively effective as regards a particular compound, the making of water-based cement calls for using different types of emulsifiers.
Tests show that the presence of large quantities and different types of emulsifiers may impair the adhesive strength of the cement, hence the strong demand for water-based cement emulsifiers that are effective over a wide range of ingredients, to reduce both the quantity and the number of types of emulsifiers used.
The Applicant has surprisingly discovered a particular class of emulsifiers that is universally effective over the various ingredients of water-based cement.
According to the present invention, there is provided a water-based cement for producing tyres, comprising water as solvent, a cross-linkable unsaturated-chain polymer base, sulphur, reinforcing filler, zinc oxide, and accelerators; said cement being characterized by comprising an emulsifier of the general formula (I)[R1R2R3NR5(N(R4)3)n](n+1)+(n+1)X−  (I)
where:
X is an anionic atom or group
R1, R2 and R3, which may be the same or different, are each CmH2m+1, where m ranges between 1 and 3, or CH2CHCH2 or CHCHCH3 
R4 is CH2CHCH2 or CHCHCH3 
n is 0 or 1
R5 is an aliphatic group C15-C22 when n is 0; and is an aliphatic group C8-C16 when n is 1
when n is 0, at least one of R1, R2, R3 and R5 comprises a double bond.
Preferably, the water-based cement comprises by weight 5 to 80% of water, 10 to 60% of a cross-linkable unsaturated-chain polymer base, 0.2 to 1% of sulphur, 1 to 25% of reinforcing filler, 0.1 to 3% of zinc oxide, and 0.1 to 1% of accelerators; said cement being characterized by comprising 0.1 to 10% of an emulsifier of the general formula (I).
Preferably, R1, R2 and R3 are CH2CHCH2.
Preferably, R1, R2 and R3 are CH2CHCH2, R5 comprises a double bond, and n is 0.
Preferably, R1, R2 and R3 are CH2CHCH2, n is 1, and R5 is a saturated aliphatic group.
Preferably, the quantity of emulsifier in the cement ranges between 0.5 and 5% by weight.
The examples below are purely indicative and non-limiting, for a clearer understanding of the invention.